In the past few years interest in stem cells as potential therapeutic agents has exploded, due in part to the recognition that stem cells are present in a myriad of tissues in the adult, and that these adult somatic stem cell populations are pluripotent. We have been studying two stem cell populations, blood-derived and keratinocyte stem cells. In Aim I we will examine the extent to which blood-derived cells are involved in wound healing by determining the contribution Of endogenous blood-derived cells to injured and uninjured skin in non-diabetic and diabetic mice. This will be accomplished by making skin wounds in hematopoietic chimeric mice (mice whose endogenous hematopoietic system has been replaced with cells that can be distinguished from those of the host). Wounds will be evaluated using histology, immunohistochemistry, and morphometry. Our hypothesis is that diabetes reduces the normal contribution of blood- derived cells to structures in the skin, especially during wound healing. If this hypothesis is correct, additional experiments in this aim will begin to delineate the mechanisms responsible for the reduction. In the second part of this proposal we will test whether blood-derived or keratinocyte stem cells can be used therapeutically to augment wound healing in a mouse model of diabetes. For this we will test whether addition of subsets of blood cells or epidermal stem cells accelerate wound healing in non-diabetic and diabetic mice. Our hypotheses are that addition of exogenous blood-derived or keratinocyte stem cells can accelerate wound healing, and that this effect will be more pronounced in diabetic than in non-diabetic mice. We also hypothesize that both blood-derived and keratinocyte stem cell populations are multipotent and will contribute to a variety of cell types in the wounds. Dil labeled leukocytes, DiO labeled skin keratinocyte stem cells, or both will be injected directly into the wound beneath the scabs of skin wounds in non-diabetic and diabetic nude mice. At various times thereafter, wounds will be harvested and examined histologically and immunohistochemically to assess the rate of wound healing. We will also investigate whether diabetes affects the incorporation of these labeled cells into different skin components.